1. Field of the Invention
The present invention reelates generally to the field of content addressed storage. More specifically, the present invention is related to a logical block addressing (LBA) and logical unit number (LUN) interface for the manipulation of reference data.
2. Discussion of Prior Art
The benefits of content addressed storage (CAS) have long since been known and have been used to store, access, and protect reference data. CAS has been devised to manipulate this class of data known as reference data. Reference data refers to data that is written once and infrequently retrieved. Examples of data that fall in this class include x-rays, photos and videos, land titles, and financial documents. Reference data differs from transactional data in that reference data is not updated or retrieved with any sort of regular frequency. CAS relies on a scheme that hashes input reference data content to generate a unique object identifier.
With CAS, the write-once property is easily enforced if an object is modified, then it is stored as a new object because input reference data content will hash to another unique object identifier. Duplicates are also easily detectable since a user inputting reference data content identical to content already stored on the system will receive an identical object identifier. If an identical object identifier is received, then a duplicate object will not be created. CAS also allows the verification of the content of stored objects during retrieval. When an object is retrieved, its content is rehashed and checked against a previous hash, generated when the object was initially stored. CAS also has a larger address space than an LUN/LBA interface.
Logical block addressing (LBA) is a method used to translate cylinder, head, and sector information of a disk drive into addresses that can be used by an operating system during boot-up. Logical unit number (LUN) refers to a unique number given to each peripheral device connected to a common bus. Commands sent to a particular type of bus (e.g., SCSI) distinguish devices on the basis of their LUNs.
The CAS interface was initially proposed by Quinlan et al in “Venti: A new Approach to Archival Storage” paper. Although CAS provides many benefits, a CAS interface also requires overlaying applications to be re-written using CAS API or using an OID interface, both of which mandate a change in the implementation of existing applications. This is in opposition to the more traditionally used LUN/LBA interface.
US 2003/0001900 A1 discloses a method for executing one or more operations in a computer for interfacing an associated user with a knowledge portal that is operatively associated with a plurality of data objects in a data store. Cabanes et al. also discloses a user interface method that includes the steps of receiving user input; updating, based on received user input, one of a current object identity, a preview object identity, and a knowledge map parameter which is updated based on a current object identity. Storing user input requires placement of a document into context with respect to other information stored and available on an electronic information system. This method is useful in the context of searching and content classification. There is limited or no provision in this reference for content addressing or hashing and write properties including write-once, write-many, and write-many with versioning.
U.S. Pat. No. 6,292,880 discloses a method for caching information objects where information objects are stored according to the hash of an object's filename and its content. The disclosed method provides for an object store that supports multiple different versions of targeted alternates for the same name and storage of objects without content duplication. However, explicit mention of a method to write object content to a storage area, and re-write different object content in that same storage area is not made. Mattis et al. requires additional mappings from name keys to vectors of alternates as well as from content keys to object content data.
U.S. Pat. No. 4,064,494 discloses a content addressable memory that can non-destructively be read and which is adapted to respectively store true and inverse information data. While this reference provides electronic architectures supporting information storage and comparison, there is no premise for interfacing overlying applications with the electronic hardware existing on a lower level. In addition, no mention is made of a unique identifier for each piece of information data. There is also no premise for upholding a write-many with versioning property.
JP 2000285013 discloses an interface between a CPU and an SDRAM capable of quickly reading out data from the SDRAM by control similar to that of a DRAM. The disclosed device, however, fails to provide for a means of content addressing or hashing and write properties including write-once, write-many, and write-many with versioning in the English translation of the abstract.
“A Distributed Repository for Immutable Persistent Objects” by Douglas Wiebe discloses a system for manipulating system model objects that provides for transactional, write-once storage. System model objects describe the structure and versions of software and are located using an expanding ring multicast search algorithm. This reference provides for a system and software that addresses stored data by structure rather than solely content.
Whatever the precise merits, features and advantages of the above cited references, none of them achieve or fulfills the purposes of the present invention. There exists a need to provide the benefits of CAS with a write-once, a write-many, and a write-many property in a single system and method. It is also advantageous that a system and method provide a LUN/LBA to interface with existing content addressable memory systems.